1. Field of the Invention
The present invention relates to an image processing system for processing in particular an intermediate tone image.
2. Related Background Art
Recent development of image processing technology with computers has enabled computerized creation, editing, storage etc., of images such as those for printed matter.
In general such an image is composed of pixels each represented by "0" or "1", and such image is called a binary image. Images composed of characters and patterns can be satisfactorily represented by binary digitizing with a suitable threshold level, but images involving intermediate tone, such as photographs, generally require 4 to 8 bits per pixel for reproducing the intermediate tone. Such images are called multivalue images.
FIG. 1A shows an original image with intermediate tone, and FIG. 1B shows an example of binary digitization with a threshold value at a half level, for example a level "8" if the original image has 16 levels, wherein each pixel is represented by one bit, namely "1" (black) or "0" (white). FIG. 1C schematically shows a thus binary digitized image in which each pixel is represented by a block. In this case the image is represented by two-dimensional information with z=1.
FIG. 1D shows a representation of the original image of FIG. 1A by multivalue data of 16 density levels O-F. FIG. 1E is an explanatory view of the image information of multivalue data, in which each pixel is represented by four blocks or four bits.
A printer or a display unit connected to an image processing system is considered as a fixed factor in the system, and the image information can be subjected to a fixed gamma correction in the system, in consideration of the input-output characteristic or gamma characteristic of such output equipment. This is an important factor in handling multivalue images. For example, in order to obtain a satisfactory display on a cathode ray tube with data from a television camera, said data may be gamma corrected in consideration of the fixed gamma characteristic of said cathode ray tube. However, if such data from the television camera are directly printed, there may be obtained an unsatisfactory printout with a poor contrast, since the data are not matched with the gamma characteristic specific to the printer. In such case, a proper print can be obtained if a gamma correction is made according to the gamma characteristic of the printer. However such system can only work with predetermined input/output equipment, and will have no adaptability to other equipment.
In practice, however, the equipment to be connected to the system is often changed and should preferably be variable. Also, in the case of an image output at another terminal through a local area network, the characteristic of such terminal is generally not known.
On the other hand, each piece of equipment constituting the system, such as an input or output unit, is generally expensive, so that the entire system will become expensive if the efficiency of use of such equipment is low. For example, a scanner/printer terminal may also be used as a copying machine in off-line mode, in order to improve the efficiency of use. However, particularly when multivalue data are involved, gamma correction becomes a serious problem as explained above, if a terminal is used as an off-line copying machine as well as an on-line image output unit, or if the input and output units are variable, or if plural units are simultaneously connected to the system. In summary the system should execute image processing regardless of the gamma characteristic of the equipment connected thereto, and, in the case of off-line mode, should execute a gamma correction according to the terminals to be connected. It therefore becomes a serious factor when and where to effect the gamma correction, in consideration of the number and nature of the units of input and/or output equipment, in the off-line mode or in the on-line mode. For the purpose of matching the data with a destination terminal, a technology for varying the resolving power according to said terminal is already disclosed in a copending application Ser. No. 658,760 filed Oct. 9, 1984, assigned to the same assignee.